1. Field of the Invention
The present invention relates to a turn signal switch to be used as a direction indicator, which is attached to a steering column of an automobile or the like, and more particularly, to a canceling mechanism for causing a control lever provided for a turn signal switch to automatically return to the neutral position.
2. Description of the Related Art
In a turn signal switch for an automobile, the base end of a control lever is turnably supported in a housing that is incorporated with a steering column or the like, and the leading end of the control lever is turned from the neutral position to the right-direction indicating position or the left-direction indicating position, thereby causing a left-turn lamp or a right-turn lamp to blink.
In order to hold the control lever at three positions, the right-direction indicating position, the left-direction indicating position, and the neutral position, in the turn signal switch, a cam portion is formed on the inner surface of the housing, and a driving element is provided in the control lever via a spring so as to be engaged with the cam portion. A canceling mechanism is also provided to cause the control lever, which has been turned in the right-direction indicating position or the left-direction indicating direction, to automatically return to the neutral position when the steering wheel is turned in the direction opposite from the indicating direction.
FIGS. 10 to 16 illustrate a canceling mechanism of a turn signal switch previously proposed by the present applicant (see European Patent No. 0 778 176 A2). FIG. 10 is an exploded perspective view of the turn signal switch, as viewed from below, FIG. 11 is a perspective view showing how a first holder is incorporated into a case, FIG. 12 is a perspective view showing how a first lever member and a press spring are further incorporated in the state shown in FIG. 11, FIG. 13 is a perspective view showing how a second lever member is further incorporated in the state shown in FIG. 12, FIG. 14 is a perspective view showing how a cover is incorporated in the state shown in FIG. 13, FIG. 15 is a plan view of the turn signal switch in the neutral state, from which the cover is removed, for illustrating the operation thereof, and FIG. 16 is a plan view of the turn signal switch, from which the cover is removed, in a state in which the control lever is switched to the right-turn or left-turn direction, also for illustrating the operation thereof.
The canceling mechanism of this turn signal switch mainly comprises a case 121 attached to a steering cover (not shown), first and second holders 131 and 141 contained in the case 121, first and second lever members 151 and 161 placed on the upper surface of the first holder 131, and a cover member 171 for covering the top opening of the case 121.
As shown in FIG. 11, the case 121 includes a recessed portion 122 for containing the first holder 131, which recessed portion 122 is opened on one side and has a pair of cam faces 123, forming a depression at the center, on the other side face; and a stepped portion 124 formed at a lower position than the top end face of the case 121. Two pins 125 and 126 are provided at a predetermined interval on the upper surface of the stepped portion 124, and a slot 127 is formed at about the midpoint therebetween. High portions 123a and 123b are formed at the ends of the cam faces 123, and a retaining hole 128 is formed in the recessed portion 122 on the side opposite from the side of the cam faces 123.
The first holder 131, which is opened on one side, is inserted in the recessed portion 122 so that it can pivot horizontally. The first holder 131 has, on the side opposite from the open side, a driving element support portion 134 in which a driving element 132 is inserted. The driving element 132 is slidably inserted in the driving element support portion 134 via a spring 133, and the leading end thereof is always pressed against the cam faces 132 by the spring 133.
The first holder 131 has retaining pins 135 and 136 on the upper and lower surfaces on the open side, respectively, and a retaining groove 137 on the upper surface on the side of the driving element support portion 134. The first holder 131 also has retaining holes 138 formed in the right and left side faces on the open side.
The second holder 141 is approximately T-shaped so that a head portion 142 intersects one end of a base portion 143 at right angles. Retaining pins 144 stand at both ends of the head portion 142 so as to be rotatably passed through the retaining holes 138 of the first holder 131. The base portion 143 is inserted in an open end portion of a control lever 145, and is fixed by a spring pin 146.
The first lever member 151 is placed on the stepped portion 124 so that a retaining pin 152 standing on the lower surface thereof is loosely fitted in the slot 127 formed in the upper surface of the stepped portion 124. The first lever member 151 also has an engaging projection 153 that projects outside the case 121. The engaging projection 153 engages with a projection 183 provided in a canceling cam 182 that turns together with a steering shaft 181, as shown in FIGS. 15 and 16. The first lever member 151 also has a receiving portion 154 on the upper surface on the side of the engaging projection 153, and an engaging pin 155 on the opposite side.
After the first lever member 151 is placed on the stepped portion 124 of the case 121 so that the engaging pin 152 is loosely fitted in the slot 127, a spring member 156 is mounted so as to regulate the first lever member 151 on the stepped portion 124, as shown in FIG. 12. The spring member 156 includes a pair of winding portions 156a that are arranged at a slightly longer interval than that between the two pins 125 and 126, and end portions 156b that extend inward from the winding portions 156a, respectively, so as to intersect each other, and that are rounded at the end.
The winding portions 156a of the spring member 156 are fitted on the two pins 125 and 126 so that the end portions 156b abut on the receiving portion 154, whereby the part of the spring member 154 between the winding portions 156a is bent toward the end portions 156b, and the first lever member 151 is supported while being urged toward the outside of the case 121.
The second lever member 161 has a cam hole 162 with an angular cam side 162a on its upper surface, and a pair of support projections 164 which project from its back surface on the side opposite from the cam side 162a so as to support both ends of a coil-shaped action spring 163.
The support projections 164, which are holding the action spring 163, are inserted in the retaining groove 137 of the first holder 131, and the retaining pin 155 of the first lever member 151 is inserted in the cam hole 162 from below.
The cover member 171 covers the top opening of the case 121, and the retaining pin 135 of the first holder 131 is inserted in a retaining hole 172 formed in the upper surface of the cover member 171, thereby allowing the first holder 131 to reliably pivot on the retaining pins 135 and 136.
Next, a description will be given of the operation of the canceling mechanism in the turn signal switch. When the control lever 145 is in the neutral position, as shown in FIG. 15, the engaging pin 155 of the first lever member 151 is in contact with the top of the cam side 162a of the second lever member 161, and the retaining pin 152 is retracted by a distance that is defined by the slot 127 against the spring member 156. Therefore, the engaging projection 153 of the first lever member 151 is also retracted outside the locus of turning of the projection 183 of the canceling cam 182 that turns together with the steering shaft 181.
Even when a steering wheel (not shown) is turned in this state, the projection 183 of the canceling cam 182 does not make contact with the engaging projection 153 of the first lever member 151, and the first and second holders 131 and 141 and the control lever 145 remain in the neutral position.
When the control lever 145 is turned from the neutral position in the direction of the arrow B in FIG. 15, the first holder 131 also turns about the retaining pin 135 in the counterclockwise direction, as shown in FIG. 16. The driving element 132 at the leading end of the first holder 131 thereby passes over the high portion 123a of the lower cam face 123 in the figure, and is retained thereat. Therefore, the second lever member 161 is also kept in that position as well as the first holder 131 and the control lever 145, and, for example, a left-turn signal switch (not shown) is activated by the first holder 131.
With the turn of the second lever member 161, the engaging pin 155 of the first lever member 151 is moved along the upper slope of the cam side 162a of the second lever member 161 in the figure. This movement is reliably made because the end portions 156b of the spring member 156 elastically press the receiving portion 154 of the first lever member 151 leftward in the figure.
By the movement of the first lever member 151, the engaging pin 152 thereof makes contact with the opposite side (the left end in FIG. 16) of the slot 127, thereby stopping the movement of the first lever member 151. In this state, the engaging projection 153 of the first lever member 151 is also advanced inside the turn locus of the projection 183 of the canceling cam 182, as shown in FIG. 16.
The state shown in FIG. 16 is maintained by the press of the driving element 132 by the spring 133 at the position beyond the high portion 123a of the cam face 123. When the steering wheel shaft 181 is turned in reverse (in the direction of the arrow of FIG. 16) by reversing the steering wheel in this state, the projection 183 of the canceling cam 182 makes contact with the engaging projection 153.
When the engaging projection 153 is pushed, the first lever member 151 turns counterclockwise about the engaging pin 152 in a manner similar to a lever, the engaging pin 155 makes contact with and presses the side end (the upper part in the figure) of the cam hole 162, thereby turning the second lever member 161 and the first holder 131 about the retaining pin 135 in the counterclockwise direction. During the turn of the second lever member 161 and the first holder 131, the driving element 132 is caused to pass over the high portion 123a of the cam face 123. Then, the driving element 132 is returned to the neutral position between the two cam faces 123 by the spring force of the spring 133, and the first holder 131 and the control lever 145 also return to the neutral position shown in FIG. 15.
In the conventional turn signal switch, as shown in, for example, FIG. 16, the spring member 156 includes the pair of winding portions 156a to be fitted on the two pins 125 and 126, and the end portions 156b extending inward from the winding portions 156a so as to intersect each other, and both the end portions 156b are in elastic contact with the side face of the receiving portion 154.
In this way, the first lever member 151 is always pressed at two points by the end portions 156b of the spring member 156. Since the end portions 156b do not always have the same pressing force (spring force), the position of the first lever member 151 is not fixed, and as a result, the canceling point is not fixed. Furthermore, when the end portions 156b have different pressing forces (spring forces), the parts, e.g., the engaging pin 155, undergo localized wear, which hinders smooth operation, causes unreliable cancellation, and produces unusual noises.